Thyratron firing circuit



May 7, 1963 R. E. TAYLOR THYRATRON FIRING CIRCUIT Filed Dec. 50, 1960 DE TON/170R 22 Fla. 1. i v

FIG 30 FIG. 3b.

FIG. 30.

FIG. 30'.

Voltage 02 Capacifor 20 Input to Terminal 32 Voltage of Pol'nf A Voltage at Detonator 28 0 INVENTOR RALPH EDWARD TAYLOR BY Xj. Q0114 C2. JQWM 3,088,4lfi Patented May 7, 1953 THYRATRON FIRING CIRCUIT Raiph E. Taylor, Silver Spring, Md., assignor to the United grates of America as represented by the Secretary of the rmy Filed Dec. 30, 1960, Ser. No. 79,937 3 Claims. (Cl. 102--70.2) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to firing circuits for electronic fuze systems employed in ordnance missiles.

The component circuits of electronic fuzes must be as compact and efiicient as possible due to the severe space limitations and high reliability requirements imposed by the missile environment. Accordingly, the firing circuit must deliver to the detonator a firing pulse of maximum energy content .in order to reduce as far as possible the output requirements for the fuze battery power supply.

An object of this invention is to provide an ordnance fuze firing circuit which produces a high energy firing pulse.

A further object of this invention is to furnish an improved firing circuit having low output impedance characteristics.

Another object is to provide improved switching action in a fuze firing circuit for more efiicient coupling of its firing pulse to the detonator.

The specific nature of the invention, as well as other objects, uses, and advantages thereof, will clearly appear from the following description and from the accompanying drawing, in which:

FIG. 1 is a schematic circuit diagram of a firing circuit in accordance with this invention.

FIG. 2 is a graph of the response characteristic of a Zener diode of the type employed in this invention.

FIGS. 3a 3d are graphs showing voltage waveforms at identified points in the firing circuit of FIG. 1.

FIG. 1 .shows a firing circuit containing a thyratron which has a plate 11, control grids 12 and 13, and a cathode 14. The B+ power source for the fuze system is indicated diagrammatic-ally at terminal 30. The plate 11 is coupled to terminal 3% by means of resistor 18 to provide operating voltage for thyra-tron 10. An energy storage capacitor 2% is connected between plate 11 and circuit ground. The cathode is directly connected to grid 12 and further connected through an output resistor 22 to circuit ground. A fuze system (not shown) is connected by means of an input terminal 32 to the control grid 13 of thyr-atron It The associated fuze system may be any one of the several types well known in the art producing an electrical trigger signal when the missile reaches a desired position with respect to a target. The details of the fuze form no part of the instant invention. A resistor 16 is connected to terminal 30 at one end and to cathode 14 at its other end. Resistors 16 and 22 form a voltage divider for impressing a biasing potential upon cathode 14 to maintain thyrat-ron 10 normally nonconductive. The junction of resistors 16, 22 and cathode 14 is labeled point A in FIG. 1.

A Zener diode 24 and the fuze detonator 28 are connected together in series between point A and circuit ground. The Zener diode 24 is a semiconductor diode, preferably a silicon diode, comprising a rectifying pn junction formed by an integral body of semiconductive material having a body portion 25 of n-type material and a body portion 27 of p-type material. This device acts as a rectifier preventing appreciable current flow in the reverse direction from 25 to 27 when the reverse voltage is below a predetermined breakdown voltage. FIG. 2

illustrates the voltage-current characteristic of diode 24. When the reverse voltage exceeds the critical voltage e of FIG. 2, the diode 24 breaks down and permits current to flow freely in the reverse direction, the voltage drop across the diode being maintained at e Due to the connection of the n-type body portion 25 to point A, the Zener diode 24 is poled to present its reverse impedance to the voltage across output resistor 22.

In operation, when the missiles battery power supply is activated a predetermined time after launching, full plate voltage appears at terminal 30. Accordingly, the plate energy storing capacitor 20 is charged through resistor 18. The time required to charge capacitor 20 may be employed as the safing and arming time delay, if desired, since the detonator 28 cannot be fired in this interval even if thyratron 10 prematurely conducts. However, in order to prevent spurious ignition of thyratron 10, the volt-age divider formed by resistors 16 and 22 biases cathode '14 positively with respect to control grid 13. The thyratron 10 is maintained nonconducting until a trigger signal at terminal 32 overcomes the bias of point A.

The reverse breakdown voltage e of the Zener diode 24 is made somewhat higher than the cathode bias at point A. Therefore, this bias is effectively blocked from the detonator 28, due to the very high reverse impedance of Zener diode 24 in series with detonator 28. The blocking action thus obtained is necessary to prevent immediate functioning of detonator 28 by the bias voltage.

FIG. 3b shows the aforementioned trigger signal generated at time t by the associated fuze system. In FIGS. 3a-3d, the voltages shown for the interval t t represent circuit conditions after the arming delay when capacitor 20 is charged substantially to e The trigger pulse initiates conduction of thyratron 10 in a well known manner, allowing energy storing condenser 20 to discharge rapidly through thyratron 10 and output resistor 22. Capacitor 2t) discharges in the manner illustrated in FIG. 3a during the interval t t The voltage drop across resistor 22 due to the capacitors discharge is superimposed upon the cathode bias, as shown in FIG. 3c. When the resulting voltage at point A exceeds the breakdown voltage e of Zener diode 24, the diode presents a very low impedance between point A and detonator 28. Thus, the firing pulse developed across output resistor 22 is directly coupled to the detonator 28 to function the fuze warhead. The selective switching action of the Zener diode permits substantially direct connection to the detonator upon triggering of the firing circuit and blocking of the required cathode bias prior to triggering. The low impedance of Zener diode 24 in its reverse breakdown state provides elficient coupling of the firing pulse energy from capacitor 20 to the detonator 28.

At time t the firing pulse amplitude has decreased sufiiciently sothat the voltage at point A is less than 2 Diode 24 is switched to its high impedance state, sharply terminating the firing pulse as shown in FIG. 3d.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement the scope of the invention as defined in the appended claims.

I claim as my invention:

1. 'In an ordnance fuze firing circuit, a thyratron including an anode, a cathode and at least one control grid, a source of electrical energy, said source including an energy storing condenser connected between said anode and ground, input means for applying a trigger signal to said control grid, a resistor connected from said cathode to ground, means for applying a biasing potential to said cathode, a detonator, and a Zener diode connected between said cathode and said detonator, said Zener diode being poled so that said biasing potential is blocked from said detonator.

2. An ordnance fuze switching circuit for applying a firing pulse to a detonator in response to a trigger signal comprising, in combination: a thyratron having an anode, a cathode and a control grid, a 13+ voltage source, a resistor connecting said anode to said source, an energy storage capacitor connected between said anode and circuit ground, means for applying said trigger signal to said control grid to ignite said thyratron, an output resistor connected from said cathode to ground, means for applying a positive biasing potential to said cathode, a detonator, and a Zener diode connecting said detonator to said cathode and poled to present its reverse impedance at said cathode to block said biasing potential from said detonator, the breakdown voltage of said Zener diode being higher than said biasing potential but lower than the voltage across said output resistor when said thyratron is ignited.

3. In an ordnance fuze firing circuit, an electrical power source, a thyratron with a plate, a cathode and a 10 bias is blocked from said detonator.

References Cited in the file of this patent UNITED STATES PATENTS 2,874,333 Gr-ay Feb. 17, 1959 2,897,759 Hinman Aug. 4, 1959 2,998,774 Gibson Sept. 5, 1961 3,011,096 Wallack et a1 Nov. 28, 1961 3,022,446 Irish Feb. 20, 1962 

1. IN AN ORDANCE FUZE FIRING CIRCUIT, A THYRATRON INCLUDING AN ANODE, A CATHODE AND AT LEAST ONE CONTROL GRID, A SOURCE OF ELECTRICAL ENERGY, SAID SOURCE INCLUDING AN ENERGY STORING CONDENSER CONNECTED BETWEEN SAID ANODE AND GROUND, INPUT MEANS FOR APPLYING A TRIGGER SIGNAL TO SAID CONTROL GRID, A RESISTOR CONNECTED FROM SAID CATHODE TO GROUND, MEANS FOR APPLYING A BIASING POTENTIAL TO SAID CATHODE, A DETONATOR, AND A ZENER DIODE CONNECTED BETWEEN SAID CATHODE AND SAID DETONATOR, SAID ZENER DIODE BEING SO THAT SAID BIASING POTENTIAL IS BLOCKED FROM SAID DETONATOR. 